A variety of post mold preform transfer methods are currently employed on injection molding machines to optimize the cycle time of the molding machine. Some parts (for example plastic preforms) are typically injection-molded using PET resin, and can have a wall thickness varying from about 2.00 mm to greater than 4.00 mm, and require extended cooling periods to solidify into substantially defect-free parts. Heavy walled parts (such as those made from a material that has a high resistance to thermal heat transfer, like plastic resin) can exhibit “reheating” phenomena that can produce defective parts after they have been ejected from the mold.
Several techniques are employed to perform a post mold cooling function, wherein partially cooled preforms are ejected from the injection mold after an initially cooled surface skin has formed to allow the part to be ejected without deformation. The partially cooled preforms are then handed off to a downstream device that continues to hold the preform while removing the remaining heat so that the preform can subsequently be handled without damage. Typically, the preform surface temperature needs to be lowered to about 70° C. to ensure safe handling.
The early ejection of partially cooled preforms releases the injection molding equipment earlier in the molding cycle, thereby significantly improving the production efficiency of the equipment. The apparatus for removing the hot molded part from the take-off plate must handle the hot preform without damaging it.
U.S. Pat. No. Re. 33,237 discloses a robotically-controlled multi-position take out plate for removing partially cooled injection molded parts from the core side of an injection mold. The parts are ejected from the mold directly into cooled carriers, as disclosed in U.S. Pat. No. 4,729,732, and transported by the robot to an outboard position where some of the parts are ejected onto a conveyor. The plate has multiple sets of carriers, each set being sufficient in number to hold one part from each of the cores of the multi-cavity mold. There are multiple sets of carriers on the plate so that multiple sets of molded parts can be held and cooled, the set that is ejected being the set that has been cooling the longest in the tubes of the plate. The disclosed method of ejecting the parts relies on the termination of a vacuum that is holding the parts in the carriers, thereby allowing gravity to cause the parts to fall out when the take out plate has been rotated 90 degrees to a discharge position. Without a positive ejection force, parts can stick in the tubes and cause jamming of the machine.
U.S. Pat. No. 5,447,426 teaches unlocking preforms by using ejector bars.
U.S. Pat. No. 6,171,541 discloses inserting a cooling pin into the interior of a partially cooled part to discharge a cooling fluid therein to assist cooling. Also disclosed is a procedure to apply a vacuum through the same cooling pin to cause the part to remain attached to the pin when it is moved away from the carrier holding the part, thereby removing the part from the carrier. The pins, mounted to a frame, are then rotated 90 degrees to a discharge position and the vacuum terminated to allow the parts to fall off the pins. There is no disclosure of grippers for grasping an external surface of the parts to hold and transport a part.
U.S. Pat. No. 4,836,767 discloses a rotatable table mounted on the moving platen on which is mounted two core sets for the mold. While one core set is in the closed mold position for injection molding parts, the other is positioned outboard for ejecting the parts into cooled carriers that are mounted on an indexable, four-sided carousel that is mounted to the stationary platen of the machine. Four sets of molded parts can be carried on the carousel allowing an extended cooling time to be performed. The parts remain on the cores for one additional cycle time sequence that provides a small extension of cooling time of the interior of the parts before they are transferred to the carousel.
U.S. Pat. No. 3,804,568 discloses a robot mounted to the moving platen of an injection molding machine, wherein the robot drives a take out plate into and out of the open mold area to remove ejected parts. A second transfer plate then unloads the take out plate while it is in the outboard position. The motion of the moving platen is used, via cams and linkages, to actuate the take out plate vertical motion and to synchronize it mechanically so that there is no risk of collision with the mold during its operation.
U.S. Pat. No. 5,354,194 discloses a molded part removal unit mounted to the side of the fixed platen.
An earlier Husky preform molding system used a robot with a single position take out plate with carriers to unload PET preforms. The robot was mounted on the stationary platen and moved the take out plate vertically. In the outboard position, above the mold, a vacuum tube carrier of a transfer plate was aligned with the carriers and removed the molded parts therefrom by application of vacuum to their interiors. The transfer plate moved to a second outboard position at the non-operator side of the machine and rotated to allow the parts to drop from the tubes when the vacuum was terminated.
Copending Husky U.S. published application 2004/0185136 published Sep. 23, 2004 describes a molded part handling apparatus for an injection molding machine having a fixed platen and a moving platen. A take off device is coupled to the fixed platen and configured to remove molded parts from between the fixed platen and the moving platen. A cooling device is coupled to the moving platen and configured to cool the molded parts carried by the take off device.